Geth v1.8.20 is a bit of a special release. On one hand it's the release that finally enables the Constantinople hard fork on mainnet at block 7080000 (and Rinkeby at block 3660663). It's also our last planned release of the 1.8 family (we'll still do hotfixes if need be), meaning that we'll start merging backwards incompatible changes onto master in preparation of Geth 1.9.0 (we don't have an ETA for it, but January the earliest).